1. Field of the Invention
The present invention relates in general to a substrate heater installed in a reactor of a chemical vapor deposition equipment and used for heating a substrate or a susceptor and, more particularly, to a structural improvement in such a heater for heating the substrate or the susceptor to a high temperature while improving the heating efficiency.
2. Description of the Conventional Art
Recently, a variety of elements such as metals, ceramics, semiconductors, superconductors and plastics are produced through chemical vapor deposition processes in accordance with development of chemical vapor deposition techniques.
In the chemical vapor deposition process, the performance of the resulting products are influenced by how efficiently the substrate or the susceptor is heated by a heater. The heater is thus regarded as a very important element of the chemical vapor deposition equipment.
In the typical chemical vapor deposition equipment, the substrate is laid on a flat susceptor within a reactor and heated by a heater provided in a lower section of the susceptor. The shape of the heater should thus be flat. In addition, the susceptor is rotatable in order to achieve desired even heating of the substrate laid upon the susceptor. With the rotatable structure of the susceptor, the heater should not interfere with the rotating motion of the susceptor, and this restricts designing of the heater.
When the reactor of the chemical vapor deposition equipment is made of a ceramic material such as quartz, the substrate is not heated by the typical heater but is heated through high frequency heating. However, the use of high frequency heating is attended by limitation upon the reactor size and requires provision of thorough shielding for prevention of leakage of electromagnetic waves. Therefore, use of the chemical vapor deposition equipment using the high frequency heating undesirably increases the production cost. Another problem of the above chemical vapor deposition equipment is that it is large in size and, as a result, occupies a large space. Representative examples of typical materials for the heater of the chemical vapor deposition equipment is a kanthal wire or a nichrome wire. However, such a typical material for the heater is limited in its use in accordance with gases introduced into the reactor of the equipment and, furthermore, scarcely heats the substrate to a temperature higher than 1000.degree. C.
There has been proposed another type of heater. In order to produce this heater, a thin graphite plate is appropriately machined and, thereafter, coated with either PBN (pyrolyric boron nitride) or SiC. The PBN or SiC coated graphite plate is, thereafter, holed at its center so as to form a rotating shaft hole for receiving a susceptor rotating shaft therein, thus to allow rotation of the susceptor. This heater, however, requires a particular technique in the connection of its electrodes, thus making the production process complicated. Another problem of this heater is that the heater, while being very expensive, nevertheless has a low impact resistance.